Belgrade, Serbia — Serbia's most skillful politician rarely smiles, doesn't socialize, and believes religiously in a special destiny for Serbia. Now, Prime Minister Vojislav Kostunica is shaking Serbia's newly elected government – over the destiny of Kosovo.

Days after 2.2 million Serbs voted to join Europe by reelecting President Boris Tadic, Mr. Kostunica is playing a high-stakes game that has helped paralyze the government. He has accused the European Union of "jeopardizing the territorial integrity … of Serbia" as it prepares to send a mission to Kosovo, and blocked Mr. Tadic from signing an EU premembership agreement – saying it is a European quid pro quo for Kosovo's independence from Serbia.

The result could be to boost the radical leadership Serbia just voted narrowly against, analysts say – and promote policies that Europeans worry could destabilize the Balkans. Before elections, some analysts felt the government might fall if pro-Russia radical Tomislav Nikolic was elected. Now the way may be paved anyway by a statesman who is showing a talent akin to that of former hard-line Serbian President Slobodan Milosevic – whom he helped oust – for writing Serbia's script from behind the scenes, analysts say.

Just last spring, Kostunica used his fabled power-broking skills to halt a parliamentary takeover by hard-line nationalists. Now, Kosovo Albanians say, he is frightening Europe in a bid to delay independence, something Serbia has done successfully for two years under Kostunica.

Diplomats do grudgingly admire Kostunica's skills. Liberals here whisper he is twice as clever as Tadic and twice as dangerous as Mr. Nikolic.

In just over a year, Kostunica has resurrected the emotional volcano of Kosovo, invented a new relationship with Russia, given a green light to disaffected radicals, rewritten the Constitution, and made himself the center of politics – at a time when his approval rating has dropped from 81 percent in 2000 to 7.5 percent today. A popular Belgrade cartoon, made after Kosovo Albanians elected Hacim Thaci as prime minister in November, shows Kostunica next to Mr. Thaci, who says, "I won 40 percent and will be prime minister." A bubble above Kostunica has him thinking, "That's the easy way!"

Kostunica interlocutors describe him as sympathetic in his early days in power. But they say he has shifted from the anticommunist legal scholar who ran a small think tank in Yugoslavia to a democrat opposed to Milosevic to a power-seeker drenched in Serbian patriotism. "I found him very agreeable, very refreshing in 2000," says one diplomat. But today, "It is Kostunica's fault if more and more Serbs speak of fighting for Kosovo. He's become a raving nationalist."

When Jacques Rupnik of Sciences Po in Paris first met Kostunica, the Serbian politician was reading America's Founding Fathers and studying the US Constitution. Mr. Rupnik asked if Kostunica was a nationalist or a democrat; Kostunica said he was both. "He saw himself as the true nationalist and Milosevic as an opportunistic fake," Rupnik says.

Belgrade sources say Kostunica is so private that even his inner circle does not know his real thoughts. He is not seen at social events or Belgrade's soccer stadium. His wife has ties to a high-ranking Serbian Orthodox church figure. Kostunica's father fought in World War II with the Chetniks – a guerrilla group of Serb patriots – not with Tito's multiethnic Partisans – a formative fact. Kostunica is famously dour. "[He] always looks like he's a bit fed up with everything, but that's just him," says one European diplomat.

Significantly, Kostunica has ruled out violence. "People call him a 'little Milosevic,' but I don't think that is fair," says Dejan Anastasijevic, a columnist for the weekly Breme. "He has democratic credentials. He handed over a dozen generals to The Hague. Our press is freer than before.... [H]e hasn't advocated violence, and that is where many draw the line."

Balkan analysts note that while Kostunica's Democratic Party of Serbia keeps the democratic coalition intact, his underlying policies aid the Radical Party. "Nikolic and the radicals prosper greatly under Kostunica," says James Hooper, a former US diplomat. "Kostunica believes in the solutions of Nikolic on Kosovo, minus the violence needed to achieve those aims. As soon as [former Prime Minister Zoran] Djinjic was killed, Kostunica dismantled all the reforms he established."

Tadic's reelection Sunday was seen as a setback for Kostunica. Without Tadic, Kostunica could easily control the democrats, sources say, and become the man Europe deals with on foreign affairs. Days before the polls, Kostunica tried to force Tadic to agree to nullify all EU treaty plans, Tadic's platform, if the EU sent a police mission to Kosovo, as it has voted to do. Tadic refused.

Still pursuing this aim, Kostunica has Serb politics at a standstill. He won't let the government meet, since Tadic ministers would approve the EU deal. Tadic won't let parliament meet, fearing that Kostunica will create a new coalition of radicals. Kostunica said parliament must "urgently" meet for reasons of national security, before "Albanian separatists … supported by the US and EU … declare independence unilaterally" in Kosovo.

Kostunica's tactics are "not simply rhetoric," says former US Ambassador to Serbia William Montgomery, who lives here.

In one sense, Kostunica is correct about the EU's intent, analysts say. While rarely linked explicitly, the understanding in Europe after a decade of war led by Milosevic's Serbia and ended by NATO, is that Kosovo would be independent and Serbia would be a member of the EU. That was the script until last year.

Critics say that if Europe and the US quickly accepted the desire by Kosovo's 90-percent Albanian community for independence after the war, when Serbs were tired of Milosevic, rather than deal with it nine years later in tandem with Serbia's EU status, the issue would be moot.

"It is the official policy of the Serbian government to join Europe," notes Albert Rohan, a former foreign secretary of Austria. "The EU in turn wants all the Balkan states to be members."

Kostunica's unofficial foreign policy harks back to that of Tito's Yugoslavia – balancing between East and West. He has secured Vladimir Putin's veto on Kosovo independence in the UN Security Council. Among other deals, Kostunica last month arranged to sell Serbia's oil and gas monopoly to Russia's Gazprom.